1. Field of the Invention
The present invention relates to a vehicle motion control system, and particularly to a vehicle motion control system capable of performing, in parallel, motion control based on yaw rate and motion control based on sideways slip angular velocity.
2. Description of the Related Art
Japanese Patent No. 3324965 discloses a vehicle motion control system which performs motion control based on a yaw rate deviation between a reference yaw rate determined based on a steering angle and a vehicle speed, and a detected yaw rate, when the vehicle turns in an understeer state. In addition, the vehicle motion control system performs motion control based on a sideways slip angular velocity when the vehicle turns in an oversteer state.
The oversteer suppressing control, the understeer suppressing control and the spin suppressing control of a vehicle are performed according to yaw rate deviation and sideways slip angular velocity in respective regions illustrated in FIG. 4. In the figure, there is a region where motion control based on yaw rate deviation and motion control based on sideways slip angular velocity overlap each other. Particularly, in a region where understeer suppressing control for suppressing understeer based on yaw rate deviation and spin suppressing control based on sideways slip angular velocity overlap each other, the directions of turning moment required in these controls are opposite to each other. Accordingly, when the understeer suppressing control for suppressing understeer based on yaw rate deviation and the spin suppressing control based on sideways slip angular velocity are performed in parallel to generate a turning moment, either an inward turning moment or an outward turning moment is generated depending on the situation. Thus, the driver of the vehicle has difficulty in predicting whether the motion controls will proceed in a turn accelerating direction or a turn suppressing direction, resulting in a deterioration in vehicle control performance.